Controlling transport in mixtures of interacting particles using Brownian motors

An outstanding open problem in nanoscience is how to control the motion of tiny particles. Ratchetlike devices, inspired by biological motors, have been proposed as a way to achieve this goal. However, the net directed transport is almost suppressed if the diffusing particles are weakly coupled to the underlying spatially asymmetric substrate. Here we show how adding particles of an auxiliary species, that interact with both the primary particles of interest and the substrate, provides a controlled enhancement of the flow for both species. These can move either together or in opposite directions, depending upon the strength of the interaction, and whether it is attractive or repulsive.     

Moving Wigner glasses and smectics: dynamics of disordered Wigner crystals

We examine the dynamics of driven classical Wigner solids interacting with quenched disorder from charged impurities. For strong disorder, the initial motion is plastic, in the form of crossing winding channels. For increasing drive, there is a reordering into a moving Wigner smectic with the electrons moving in separate 1D channels. These different dynamic phases can be related to the conduction noise and I(V) curves. For strong disorder, we show criticality in the voltage onset just above depinning. We obtain the dynamic phase diagram for driven Wigner solids and demonstrate a finite threshold of force for transverse sliding, recently observed experimentally.     

Tin(IV) complexes with 2-pyridineformamide-derived thiosemicarbazones: Antimicrobial and potential antineoplasic activities

Reaction of tin tetrachloride with 2-pyridineformamide thiosemicarbazone (H2Am4DH) and its N(4)-methyl (H2Am4Me), N(4)-ethyl (H2Am4Et) and N(4)-phenyl (H2Am4Ph) derivatives gave [Sn(2Am4DH)Cl₃] (1), [Sn(2Am4Me)Cl₃] (2), [Sn(2Am4Et)Cl₃] (3) and [Sn(2Am4Ph)Cl₃] (4) as products, in which an anionic thiosemicarbazone coordinates to the metal centre along with three chloride ions. The crystal structures of 1 and 2 were determined. The thiosemicarbazones were moderately active against Candida albicans and Pseudomonas aeruginosa. Upon coordination to tin(IV) the antimicrobial activity of the thiosemicarbazones increases. The studied compounds proved to be toxic to Artemia salina, suggesting that they could present cytotoxic activity against solid tumors.     

Nonlinear nanodevices using magnetic flux quanta

All devices realized so far that control the motion of magnetic flux quanta employ either samples with nanofabricated spatially-asymmetric potentials (which strongly limit controllability), or pristine superconductors rectifying with low-efficiency time-asymmetric oscillations of an external magnetic field. Using layered Bi2Sr2CaCu2O8+delta materials, here we fabricate and simulate two efficient nonlinear superconducting devices with no spatial asymmetry. These devices can rectify with high-efficiency a two-harmonic external current dragging vortices in target directions by changing either the relative phase or the frequency ratio of the two harmonics.     

Controllable coupling between flux qubits

We propose an experimentally realizable method to control the coupling between two flux qubits. In our proposal, the bias fluxes are always fixed for these two inductively coupled qubits. The detuning of these two qubits can be initially chosen to be sufficiently large, so that their initial interbit coupling is almost negligible. When a variable frequency or time-dependent magnetic flux (TDMF) is applied to one of the qubits, a well-chosen frequency of the TDMF can be used to compensate the initial detuning and to couple two qubits. This proposed method avoids fast changes of either qubit frequencies or the amplitudes of the bias magnetic fluxes through the qubit loops, and also offers a remarkable way to implement any logic gate, as well as tomographically measure flux qubit states.     

Generation and control of Greenberger-Horne-Zeilinger entanglement in superconducting circuits

Going beyond the entanglement of microscopic objects (such as photons, spins, and ions), here we propose an efficient approach to produce and control the quantum entanglement of three macroscopic coupled superconducting qubits. By conditionally rotating, one by one, selected Josephson-charge qubits, we show that their Greenberger-Horne-Zeilinger (GHZ) entangled states can be deterministically generated. The existence of GHZ correlations between these qubits could be experimentally demonstrated by effective single-qubit operations followed by high-fidelity single-shot readouts. The possibility of using the prepared GHZ correlations to test the macroscopic conflict between the noncommutativity of quantum mechanics and the commutativity of classical physics is also discussed.     

Wet granular materials

Most studies on granular physics have focused on dry granular media, with no liquids between the grains. However, in geology and many real world applications (e.g. food processing, pharmaceuticals, ceramics, civil engineering, construction, and many industrial applications), liquid is present between the grains. This produces inter-grain cohesion and drastically modifies the mechanical properties of the granular media (e.g. the surface angle can be larger than 90 degrees). Here we present a review of the mechanical properties of wet granular media, with particular emphasis on the effect of cohesion. We also list several open problems that might motivate future studies in this exciting but mostly unexplored field.

Wet granular materials

All authors

Namiko Mitarai &; Franco Nori

https://doi.org/10.1080/00018730600626065

Published online:

01 February 2007

Table     

Shape waves in 2D Josephson junctions: exact solutions and time dilation

We predict a new class of excitations propagating along a Josephson vortex in two-dimensional Josephson junctions. These excitations are associated with the distortion of a Josephson vortex line and have an analogy with shear waves in solid mechanics. Their shapes can have an arbitrary profile, which is retained when propagating. We derive a universal analytical expression for the energy of arbitrary shape excitations, investigate their influence on the dynamics of a vortex line, and discuss conditions where such excitations can be created. Finally, we show that such excitations play the role of a clock for a relativistically moving Josephson vortex and suggest an experiment to measure a time dilation effect analogous to that in special relativity.     

Simultaneous Voltammetric Determination of Lead and Tin by Adsorptive Differential Pulse Stripping Method and Orthogonal Signal Correction‐Partial Least Squares in Water Samples

An adsorptive differential pulse stripping method for the simultaneous determination of lead and tin is proposed. The procedure involves an adsorptive accumulation of lead and tin on a hanging mercury drop electrode (HMDE), followed by oxidation of adsorbed lead and tin by voltammetric scan using differential pulse modulation. The optimum experimental conditions are: 0.2 mol L^?1 HNO₃, accumulation potential of ?900 mV versus Ag/AgCl, accumulation time of 200 s, scan rate of 20 mV s^?1 and pulse height of 80 mV. Lead and tin peak currents were observed in the same potential region at about ?400 mV. The simultaneous determination of lead and tin by using voltammetry is a difficult problem in analytical chemistry, due to voltammogram interferences. The resolution of a mixture of lead and tin by the application of orthogonal signal correction‐partial least squares (OSC‐PLS) was performed. The linear dynamic ranges were 0.003‐0.35 and 0.008‐0.50 μg mL^?1 and detection limits were land 3 ng mL^?1 for lead and tin, respectively. The RMSEP for lead and tin with OSC and without OSC were 2.8737, 6.0557 and 8.0941, 9.5151, respectively. The capability of the method for the analysis of real samples was evaluated by the determination of lead and tin in water samples with satisfactory results.